Piston driven internal combustion engines typically include valve guides for guiding and supporting the reciprocating sliding motion of each of the poppet valves that may be included in the cylinder head. Such poppet valves may include, for example, intake and exhaust valves. Poppet valve guides of a conventional (i.e. known) construction are shown in FIG. 1 installed in a cylinder head and are generally indicated as 1. Each valve guide 1 includes a mounting portion 2 that is press fit into the cylinder head. The valve guides 1 also include a portion 3 that protrudes from the cylinder head. A poppet valve stem (not shown) is inserted through the void 4 in the valve guide 1, and the inner surface of the valve guide 1 supports the valve stem as it slidingly reciprocates. A steel washer, such as washer 5, may be installed about the guide 1 in engines including an aluminum cylinder head in order to provide a seat for the valve spring and prevent the spring from abrading the cylinder head.
It is desirable that the poppet valve slidingly reciprocate along a straight path, and any lateral movement of the valve stem should be minimized so as to ensure proper closure of the valve and prevent premature wear or failure of the valve stem. To inhibit such lateral movement, conventional poppet valve guides, such as valve guide 1, include a long mounting portion, such as portion 2, that typically has a length that is 3 to 4 times the diameter of the cross-section of the valve guide's valve stem-receiving void, such as void 4. The long mounting portion inhibits lateral movement of the valve stem by providing support against the bending loads imparted to the valve guide by the poppet valve itself and also by the valve actuating apparatus. The long mounting portion of conventional poppet valve guides also serves a second function by providing a large contact area between the valve guide and the cylinder head to better facilitate the transfer of heat from the poppet valve to the valve guide and then into the cylinder head and its water jacket or cooling fins.
A large contact area between the valve guide mounting portion and the cylinder head requires the provision of a correspondingly thick cylinder head. Thus, a relatively thick cylinder head is necessary with conventional poppet valve guides (such as valve guide 1) in order to properly engage and suitably support the valve guide and provide the interface between the valve guide and the cylinder head necessary for suitable heat transfer to the cylinder head. However, increasing the thickness of the cylinder head increases the space occupied by the engine and the weight and cost of the engine.
Accordingly, there exists a need for an improved poppet valve guide for internal combustion engines. More broadly, there exists a need for an improved guide for supporting and directing the sliding movement of a slidingly movable member, such as, for example, a valve.